Disadvantages associated with the measurements that take place on the drying section of the paper machine are numerous. The measurements are limited to the front side of the drying section of the paper machine with an open or a closed hood. The time-consuming measurements require equipment, which is difficult to carry, and at least two trained persons who must work in physically straining conditions. The rotating ropes and rolls with the closing nips, bad visibility and heat threaten the work safety. Further, the persons have difficulties to move due to the protective clothing that they have to wear, the heavy equipment and the construction of the paper machine. For the above-mentioned reasons, the measurements are extremely expensive.